Process and apparatus for treatment of hydrocarbons



Aug. 29, 1961 F. F. A. BRACONIER ET AL 2,998,466

PROCESS AND APPARATUS FOR TREATMENT OF HYDROCARBONS Filed May 18, 1959NVE A NTOR$ Frederic .Bmcomer BY Jean J-llERija mmmf ,l', I

A T01 EYS Uted States Patent 2,998,466 PROCESS AND APPARATUS FORTREATMENT OF HYDROCARBONS Frederic F. A. Braconier, Plainevaux, and JeanJ. L. E. Riga, Liege, Belgium, assignors to Societe Beige de LAzote etdes Produits Chimiques du Marly, Liege, Belgium Filed May 18,1959, Ser.No. 813,811 Claims priority, application Austria Aug. 7, 1953 11 Claims.(Cl. 260-679) This invention relates to a process for pyrolysis ofhydrocarbon gases and to apparatus therefor.

Unsaturated hydrocarbons, particularly acetylene, are now required in avery pure state for synthesis of organic chemicals and especially forproduction of vinyl compounds for manufacture of synthetic resins.Pyrolysis of hydrocarbons has long been known to produce suchunsaturated products, but the art has sought continually to improvepurity and yield. The pyrolysis reaction is conveniently carried out bypartial combustion of gaseous or vaporized hydrocarbons. Heat releasedby the exothermal burning of a portion of the hydrocarbon is used toraise the remainder of the starting material to an elevated temperatureat which conversion to less-saturated hydrocarbon products occurs. Thisflame pyrolysis is brought about by introducing a mixture of hydrocarbonfuel and oxygen into a reaction chamber. After partial combustion, thegases are quenched to terminate the pyrolysis reaction while asubstantial yield of the desired pyrolysis product remains, i.e., beforeit is decomposed by further pyrolysis. As the reaction is very fast,this necessitates a total reaction time measured in fractions ofseconds, and any lack of homogeneity in the feed, or lack of uniformityof reaction condtions, will impair the value of the product.

Any part of the reactants which is over-reacted or not fully reacted notonly reduces yield and efiiciency, but makes impurity in the productwhich seriously impairs its value as an intermediate for use insynthesis.

It is advantageous to preheat both pyrolysis reagents (hydrocarbon andoxygen) to the highest possible temperature before reaction. Suchpreheating reduces the number of calories which have to be supplied bypartial combustion of the feed hydrocarbon and thereby reducesconsumption of purified oxygen as Well as hydrocarbon.

Such preheating of the combustible mixture is limited by its tendency toignite spontaneously. This tendency is dependent both on theoxygen/hydrocarbon ratio and on the temperature. We have shown that, ifone is to utilize fully the advantages of preheating, homogeneity ofcomposition and temperature in the feed mixture are of great importance.

Our prior copending application, Serial No. 726,248, describes a processand apparatus in which oxygen and the hydrocarbon to be pyrolyzed aremixed first in an elongated and relatively narrow Venturi throat intowhich the oxygen is injected and then in a mixing chamber of expandingcross section, which leads to a distributor screen. The homogeneousmixture passes through the many parallel passages of the distributorinto the combustion chamber with velocity greater than the flamepropagation velocity of the mixture.

The mixing chamber in which are preheated oxygen and hydrocarbon, notyet quite thoroughly diffused together, is the place where pre-ignitionwould occur and imposes the limit on preheating. If the reagent gasesare not homogeneously mixed on leaving the outlet of the mixing zone,pre-ignition by local concentrations of excess oxygen may occur. In suchcases, for a given preheating temperature and a given flow time throughthe apparatus, there is a critical concentration of excess oxygen whichwill cause preignition. We have now found that, if the gases arecompletely mixed at once, in the injection zone, so that a mixtureover-rich in oxygen does not persist for a time long enough to effectignition, it is possible to preheat the gases to a higher temperatureand thus gain a higher et'ticiency.

Thus, it is an object of this invention further to improve the mixing ofgaseous reagents used in such pyrolysis. Another object of the inventionis to preheat the reagents to higher temperatures and to reduce the riskof spontaneous ignition in the mixing apparatus. Still another object ofthe invention is to promote the most efiicient operation of a furnaceused for partial combustion pyrolysis and to improve the purity of theacetylene product.

A feature of the present invention is the progressive injection ofoxygen into a hydrocarbon stream in several successive stages withmixing between, whereby an improved mixing of hydrocarbon and oxygengases is achieved.

Another feature is the injection of oxygen in each of said stages bymeans of several opposing jets directed across and advantageouslyperpendicularly to, the direction of flow of the hydrocarbon gases.

A further feature of the invention is the passage of the hydrocarbon andoxygen mixture through an annular chamber from the narrow zone directlyto a distributor, and through it into a reaction chamber.

A preferred type of mixing apparatus embodying our invention and forcarrying out the process of our invention advantageously comprises aVenturi consisting. of a convergent annular entrance chamber forintroducing hydrocarbon gases, an elongated, narrow, annular throat,which is the injection and mixing zone, including a plurality of smallannular expansion chambers, opposite sides of which are provided withperforations for injection of oxygen transversely into the hydrocarbon,and a divergent annular exit chamber connecting said injection zone witha distributor. Within and surrounded by said convergent and divergentchambers and said mixing zone, is a hollow central core in the form of adouble cone, one tip of which is situated at the center of thedistributor. The outer wall of said divergent chamber, which diverges inthe direction of gas flow, and that portion of the hollow core whichconverges in the direction of gas flow define between them an angle suchthat the gases are spread out evenly over the area of the distributorscreen. We have found it advantageous to use an angle of approximately14.

The process and apparatus described above produce a homogeneous mixtureof the gaseous reagents at the outlet of the elongated, narrow, mixingzone, and thus provide a homogeneous gas stream in said divergentchamber leading to the distributor. Local excessive concentrations ofoxygen within the gas mixture are thereby obviated, a conditionparticularly desirable for avoiding pre-ignition outside of the reactionchamber.

The nature of the present invention will be more clearly nndesrtood byreference to the accompanying drawings which are given for purposes ofillustration and to enable others skilled in the art to fully understandthe invention, so as to be able to modify it and adapt it for variousconditions of use.

In the drawings,

FIGURE 1 is a front view, in section, of a preferred embodiment of anapparatus for the flame pyrolysis of hydrocarbons;

FIGURE 2 is an enlarged sectional view showing a portion of the mixingzone of the apparatus of FIGURE 1 in greater detail;

FIGURE 3 is a horizontal section through a portion of the mixing zone ofthe apparatus of FIGURE 1, taken at line 33 of FIGURE 1;

FIGURE 4 is a horizontal section taken approximately 3 along line AA ofFIGURE 1, and is intended to show certain relationships of areas but notnecessarily details of construction; and

FIGURE 5 is a vertical section, taken along line 5-5 of FIGURE 2, andshowing a portion of a wall in the mixing zone of the apparatus ofFIGURE 1.

In FIGURE 1, the apparatus shown comprises annular convergent chamber11, narrow, elongated, annular mixing zone 12, annular divergent chamber13, distributor 14, and a portion only of combustion chamber 15.Chambers 11 and 13 and zone 12 surround hollow, central bipyramidal core16, one tip of which is situated at the center of distributor 14.

Hollow central core 16 is traversed throughout almost its entire lengthby conduit 17, which feeds to mixing zone 12 a portion of the oxygennecessary in the partial combustion reaction. Annular mixing zone 12 issurrounded by annular chamber 18 having conduit 19 entrant therein,through which conduit the remaining necessary oxygen is supplied. Upperportions of convergent chamber 11 are also surrounded by annular chamber20 having coduits 21 through which the hydrocarbon to be treated isintroduced. In order to assure uniform distribution, the hydrocarbonpasses through openings 22 uniformly spread around the top of chamber11. Walls 26 and 27 of core 16 and of divergent chamber 13 diverge at anangle of approximately 14 beyond the outlet from mixing zone 12.

As shown in FIGURE 2 in detail, the injection and mixing zone 12 isformed by a plurality of small annular chambers 23 sequentially arrangedand connected with each other by narrow short annular passages 24. Thewalls of chambers 23 are provided with a plurality of openings orperforations 25, through which oxygen from conduits 17 and 19 isinjected. The walls defining annular mixing zone 12 are advantageouslyslightly divergent in the direction of gas flow so that chambers 23 areof successively increasing volume. This volume increase maintains asubstantially constant flow rate by providing for the progressiveincrease in the total volume of oxygen supplied to zone 12 throughopenings 25.

During the normal operation of the furnace, preheated hydrocarbon gasesto be pyrolized are fed through conduit 21 into chamber 20 and then intochamber 11 through openings 22. As the gases approach mixing zone 12,their rate of flow increases because of the decreasing cross section ofconvergent chamber 11.

The other gaseous reagent, advantageously oxygen, is first preheated,and then introduced in two parts of substantially equal volumes throughconduits 17 and 19, respectively. The oxygen fed through conduit 17passes through central core 16 and is then injected into chambers 23through openings 25 in the wall of the core 16. The oxygen introducedthrough conduit 19 passes through chamber 18 and is likewise injectedinto said chamber 23 through the openings 25 in the outer wall. As shownin FIGURES 1 and 2, this injection is advantageously perpendicular tothe direction of flow of the hydrocarbon through mixing zone 12, and itis believed that a swirling of the gases is produced in each chamber 23.The mixing within each chamber, multiplied by the effect of passagethrough several of chambers 23, with successive expansion andconstriction of the stream, effects a rapid and complete mixing of thegases, so that a homogeneous blending of hydrocarbon and oxygen isobtained at the outlet of mixing zone 12 and throughout the divergentincreasing gas volume. This also avoids excessive pressure losses as thegases pass between difiereut parts of the system.

A particularly advantageous arrangement of openings 25 is shown inFIGURES 3 and 5 of the drawings, which figures are sectional viewsrespectively taken at 33 of FIGURE 1 and 55 of FIGURE 2. Although alarge number of openings 25 is advantageously used to inject oxygen intothe hydrocarbon, for purposes of clarity in FIGURE 3 only sixteen havebeen shown as entrant on mixing zone 12 from each of core 16 and chamber18. Advantageously, openings from core 16 and chamber 18 arerespectively opposed in pairs. As shown in FIGURE 5, openings 25 arealso advantageously staggered so that the openings in any of thechambers 23 are displaced along the circumference of the chamber so asnot to lie in the same vertical line with other openings in chambersabove or below the chamber in question.

Since the gaseous reagents have been thoroughly mixed on reaching theoutlet of mixing zone 12, chamber 13 serves only to connect the outletof mixing zone 12 with distributor 14 and as the expansion zone for theVenturi which is constituted by the converging annular chamber 11, theannular throat 12 and the diverging chamber 13. To obtain uniformdistribution of the gaseous mixture across the distributor 14, it isadvantageous to choose the dimensions of the apparatus such that thearea of a circular central portion of the distributor, defined byprojecting central core 16 on the plane of the distributor, equals thearea of a remaining annular portion of the distributor surface. As shownin FIGURE 4, a circular central portion 28 has an area equal to that ofannular portion 29.

The top angle of chamber 13, between walls 26 and 27, as shown, is 14.This, as mentioned earlier, gives an advantageous smooth spreading flowto assure uniform distribution. An angle significantly smaller than thisvalue necessitates an unwanted elongation of chamber 13. An anglesignificantly larger than 14, which results in a decrease in the length(ie.e., height) of chamber '13, may be conducive to lack of uniformityin distribution of the gases or may tend to retain gases in some zonesfor a time substantially longer than the average time of passage throughthe chamber.

The apparatus and process described above produce an intimate mixture ofhot gaseous reagents in a very short time period. Numerous tests ofsamples taken in several locations around the circular outlet of theannular zone 12 have shown the uniformity of oxygen content of themixtures.

In addition, the mixture flows through chamber 13 in a very shortperiod, due to the selection of the approximate 14 value of the anglementioned, and further due to the small volume of chamber 13, the heightof which is advantageously a little less than twice the greatestdiameter of the chamber.

Under circumstances such as these, it is possible to preheat the gaseousreagent to a higher temperature depending on the length of time thegases remain in mixing zone 12 and chamber 13. This is particularlyadvantageous to industry, since by increasing the preheating temperatureby 50 C. approximately 0.2 ton of pure oxygen and 200 to 250 cubicmeters of methane may be saved for each ton of acetylene produced bypyrolysis.

It may be helpful for understanding the device shown in the accompanyingfigures to give the dimensions of an actual embodiment which has shownparticular usefulness.

Example 1 In a preferred embodiment, the device shown in FIG- URE 1 hasa total height of 1965 millimeters between the inlet end of conduit 17and distributor 14. Conduit 17 has a diameter of mm. and is surroundedby hollow central core 16, the tip of which is situated at the center ofdistributor 14. Distributor 14 has a diameter of 430 mm. Annularconvergent chamber 11 has a height of 945 mm. and converges to anannular slit having a width of 16 mm., an outer diameter on the core 26of 136 mm. and inside diameter of the shell 23 of 168 mm. Mixing zone 12has a total height of 193 mm. and comprises 8 annular chambers 23 ofprogressively increasing volume, the first of which has a height of 15mm. and a width of 32 mm., and the last of which has a height of 15 mm.and a width of 46 mm. Said chambers 23 are interconnected by narrowannular passages 24 having a height of approximately mm. and a widthvarying from 16 mm., for that passage interconnecting convergent chamber11 with the first of chambers 23, to a width of 24 mm. for that passageconnecting the last of chambers 23 with divergent chamber 13. Mixingzone -12 is surrounded by chamber 18 through which is fed a portion ofthe oxygen consumed. Zone 12 itself surrounds central core 16 throughwhich the remaining portion of the required oxygen is supplied. Chamber48 and central core 16 are each connected with any one of each of thechamber 23 of zone 12 through seventy-two openings 25 having a diameterof 3 mm. and regularly staggered. In the illustrated embodiment thereare eight expansion chambers 23, which are thus connected with chamber18 and core 16 through a total of 1152 openings 25.

From zone 12 for contacting and mixing the reagents, divergent chamber13 extends down with a height of 830 mm. and an interior angle of 14between the top of walls 26 and 27. Said chamber 13 is used only forconnecting the mixing zone 12 with the distributor 14, the latter havinga diameter of 430 mm. and a height of 215 mm. Distributor 14 comprises aplurality of parallel passages leading to reaction chamber 15, only partof which is shown in FIGURE 1. The number of passages shown is reducedfor clearer showing. The number and diameter are such that the gaspasses through with a velocity greater than the flame propagationvelocity of the gas.

The apparatus of the preferred embodiment is made of refractorychromium-molybdenum steel, preferably an A.I.S.I. type 321 steel, asspecified in the Steel Products Manual, Number 24, of the American Ironand Steel Institute.

In the operation of this preferred embodiment, methane of 97 percentpurity (containing 2 percent of carbon monoxide and 1 percent ofnitrogen) is preheated to 650 C. and introduced under a pressure of 1.25absolute atmospheres through conduit 21 into said mixing apparatus at arate of 2150 cubic meters per hour (calculated at normal pressure andtemperature). The methane passes through annular chamber 20 and thenthrough openings 22 into convergent chamber 11. On passing into chamber11, the gas has a linear speed of approximately 90 meters per second.

Oxygen of 97 percent purity (containing 3 percent of nitrogen) ispreheated to 650 C. and introduced through conduit 17 under a pressureof 1.3 absolute atmospheres, at a rate of 550 cubic meters per hour.This oxygen, after passing through conduit 17, enters central core 16surrounding said conduit, and is then injected through the 576 openings25 in core 16 into the 8 expansion chambers 23 at a linear speed ofapproximately 140 meters per second. The remaining oxygen is fed throughconduit 19 at an equal rate of 550 cubic meters per hour, passes throughchamber 18 and is similarly injected into the 8 annular chambers 23through another 576 openings 25 and with a linear speed of approximately140 meters per second.

Under such conditions, the gaseous reagents are rapidly brought intocontact with each other and are thoroughly mixed in passing through the8 chambers 23. The resulting homogeneous mixture then passes throughdivergent chamber 13 and is uniformly distributed to distributor 6 14 insuch a manner that the throughput of the mixture entering reactionchamber 15 is substantially the same in each of the parallel passages ofdistributor 14.

After entering reaction chamber 15, the gas is slowed down to the flamepropagation velocity and is then ignited and the methane is therebysubjected to a partial combustion and pyrolysis. The flame isadvantageously stabilized by supplying additional oxygen at a rate ofapproximately cubic meters per hour distributed in small pilot jets, atthe bottom of the distributor 14.

The product gases obtained by this combustion contain approximately 7.8percent of acethylene and are produced at a rate of approximately 3,800cubic meters per hour of dry gas.

What is claimed is:

1. In a process for making acetylene of high purity by passing a streamof hydrocarbon in gaseous phase through a Venturi, feeding oxygen intothe hydrocarbon stream at the constricted throat of the Venturi inamount adapted to provide by partial combustion heat needed forpyrolysis of the hydrocarbon and passing the mixture through thedivergent chamber of the Venturi and parallel closely spaced passages ofa distributor into a pyrolysis flame maintained beyond said distributor,the improvement which comprises injecting the oxygen in jets atsuccessive locations along the throat and repeatedly constricting andexpanding the stream in the zone of the Venturi throat.

2. The process defined in claim 1 in which the oxygen is injectedthrough opposed jets on opposite sides of the expanded stream.

3. The process defined in claim 1 in which the stream is annular and thezones of expansion in the Venturi throat are toroidal and the jets aredistributed on opposite sides thereof at uniform angular spacing.

4. The process as defined in claim 3 in which the jets on opposite sidesof the toroidal expansion zones are opposed on a common angle but aredistributed along lines skew to the direction of flow of the stream.

5. In a process for making acetylene of high purity by passing a streamof hydrocarbon in gaseous phase through a Venturi, feeding oxygen intothe hydrocarbon stream at the throat of the Venturi in amount regulatedto provide by partial combustion the heat needed for pyrolysis of thehydrocarbon to acetylene, and passing the mixture through the divergentend of the Venturi and narrow parallel passages of a distributor screeninto a flame reaction therebeyond and quenching the reaction productswhen the pyrolysis has reached the desired stage, the improvement whichcomprises substantially completing the mixing of hydrocarbon and oxygento a homogeneous gas by repeated constriction and expansion of theflowing stream in the constricted throat of the Venturi, and by passagetherethrough at velocity sufliciently high to assure complete mixing,whereby local spots of high oxygen concentration are avoided in thedivergent passage of the Venturi- 6. An apparatus for uniformlydistributing a pyrolyzable gaseous mixture of hydrocarbon and oxygeninto a pyrolysis reaction chamber which apparatus comprises an annularconduit for feeding a stream of said hydrocarbon, said conduitconverging from a wide end thereof, at which said hydrocarbon isintroduced thereinto, to a narrow end, a plurality of annular injectionchambers open from the narrow end of said convergent conduit andsuccessively open into one another through constricted annular ports,through which said hydrocarbon stream successively passes, said chambershaving a plurality of perforations therein for injecting oxygeninwardly, and an annular mixing chamber open to a constricted annularport in the last of said injection chambers, said mixing chamberdiverging from said port to a pyrolysis reaction chamber and comprisinga divergent outer wall and a convergent inner wall.

7. An apparatus as in claim 6 wherein said perforations are distributedpairwise on opposing walls of said annular injection chambers.

8. An apparatus as in claim 7 wherein said perforations are distributedalong lines skew to a perpendicular to parallel planes defined by saidannular injection chambers.

9. An apparatus as in claim 6 wherein each of said plurality of annularexpansion chambers successively increases in volume.

10. An apparatus as in claim 9 wherein the inner and outer walls of saiddivergent annular chamber define an angle of about 14.

11. An apparatus as in claim 10 wherein the height of said divergentannular chamber is less than twice its greatest width.

References Cited in the file of this patent UNITED STATES PATENTS ArmorMar. 7, 1916 Lundgaard May 25, 1920 Schurs Nov. 2, 1920 Porter Oct. 25,1921 Schroeder Sept. 5, 1922 Rusch July 14, 1925 Blood Jan. 12, 1937MacQueen Nov. 12, 1957 Heller Sept. 9, 1958

1. IN A PROCESS FOR MAKING ACETYLENE OF HIGH PURITY BY PASSING A STREAMOF HYDROCARBON IN GASEOUS PHASE THROUGH A VENTURI, FEEDING OXYGEN INTOTHE HYDROCARBON STREAM AT THE CONSTRICTED THROAT OF THE VENTURI INAMOUNT ADAPTED TO PROVIDE BY COMBUSION HEAT NEEDED FOR PYROLYSIS OF THEHYDROCARBON AND PASSING THE MIXTURE THROUGH THE DIVERGENT CHAMBER OF THEVENTURI AND PARALLEL CLOSELY SPACED PASSAGES OF A DISTRIBUTOR INTO APYROLYSIS FLAME MAINTAINED BEYOND SAID DISTRIBUTOR, THE IMPROVEMENTWHICH COMPRISES INJECTING THE OXYGEN IN JETS AT SUCCESSIVE LOCATIONSALONG THE THROAT AND REPEATEDLY CONSTRICTING AND EXPANDING THE STREAM INTHE ZONE OF THE VENTURI THROAT.